So I've had an intermittent no start and ive tested the relay (stancor). Ot always has constant 12v but wont switch the power to the other side. So although it doesnt happen very often, the relay must be bad so I buy another. Hook it up and the same thing happens. The light only stays on for maybe 3 seconds. I'm getting constant 12v to one big one and nothing to the other 3 posts with the key off. With the key on, the voltage drops down to about 11.9 on the constant power and both little terminals get 12v and the other big post gets nothing. I've read that the pcm generates a ground to the little terminal?? I've never heard of this but I guess is possible. So for one, how to I bench test this old relay? Secondly what would be my issue here? Obviously it must not be the relay, so is it a wiring issue? What wores do what on this relay? Thanks

 

This should help.

 

To test the GPR's function all you need to do is apply power to the small front lug and ground the small rear lug and it should click. If it doesn't click it's bad, if it clicks but doesn't pass power through the two large lugs it's bad.

 

Your pcm is bad. Mine is too, resulting in the same conclusion youve come to conclude with..MY fix was to remove and tape up the end on the orange wire(from pcm) and run your own ground wire with a switch in the cab to activate relay...

 

Assuming my PCM is bad, where would be a reputable place to get one? I see a number of places online but dont know if there as good as OEM and I'm sure OEM is pretty pricey. Does one for an auto differ from one from a stick (my truck) thanks

 

 

If you have FORScan you can get a read out of your PCM details.
Mine is below for an example, yours will be different:

PCM - Powertrain Control Module
Part number: XU7FCC
Strategy : VNABLNB DPC-452
Copyright Ford Motor Co. 2010

The numbers in bold are what you need to know.

 

So I jumped the gpr with a ground wire. It only got around 10.8 when the plugs kicked on (it may have been cranking ot yesterday) it started up and loped pretty bad for about 10 seconds and then leveled out. It's been doing this recently but never did that before this issue. Is that something else to worry about? Or possible the gp's not getting the full 12v maybe. Once it's up to temp it runs great

 

How long did you have the glow plugs activated? If not long enough that might be the cause of your lope.

 

Length of gp's energized, oil weight and/or outside temp, all play a role

 

 

I am going to try it again before I pull this pcm, but i did have the jumper wire connected through the whole loping cycle. Probably 45 seconds and then I unplugged the jumper. I think regardless the pcm issue needs addressed. I did see online that potentially the icp could be bad causing the big lope. Something I'll also have to look into I guess

 

I suggest you take things one step at a time. Verifying the glow plugs are all operating would be first.
It gets expensive just buying parts to throw at a problem and in many cases it's something simple and inexpensive to fix.

 

If this is true, then how are your glow plugs getting power?

Which post are your glow plug bank leads attached to on the GPR? The big post that gets nothing?

This is puzzling.

The cold start idle romp sounds like an oil viscosity issue related to the current cold weather. If you haven't changed your oil to 5w-40 synthetic for the winter, it is highly recommended that you do so, and that may cure your idle romp.

Cold weather brings about multiple ailments simultaneously that can, because of their synchronous onslaught, appear inter connected, but can just as easily be coincidental. Fuel gelling can contribute to difficult starts as well.

But back to the topic at hand, this relay. If, as you said in the op, only one of the two big posts has power with the key on, where are your glow plugs pulling power from, if you say they are on?

PS... the glow plug light in the instrument cluster has no connection to, nor correlation with, how long the glow plugs are actually on, or whether or not the glow plugs are on. It is simply a "remember to wait before starting" idiot light.

 

the constant 12v is meaning that it was whatever the big lug was getting, it was around 11.8, not exactly 12v. My batteries read around 12.6-12.7 sitting there and with the key on dropped to around 11.8

as far as oil viscosity, I've ran 15-40 year round as long as I've owned the truck. I'm sure it would help going to 5w-40 but ive never had an issue at all in the past.

My glow plugs were replaced about 4 years ago with new motorcraft plugs, so while I guess it's possible for some to be bad, I dont think it's likely.

I'm not trying to throw parts at it but now that I've verified the reason the relay isnt sending ppwer is because it's not getting a ground signal leads me to believe the the PCM has to be the issue. When I figure this out, I will certainly explore the icp being possibly bad, or to thick of oil or whatever.

Again to clarify, if you haven't read all the comments. The relay was getting constant and key on ppwer but no power to the big lug for the glow plugs. I put a jumper ground wire to the small orange wire and then I had power to the glow plugs. From research on here and on the internet, it looks like the PCM is not sending the ground signal to the relay so I assume I need a PCM unless I want to run a jumper wire on a switch into the truck (which I dont perfer to do)

Also in regards to the light. I dont k ow how it works but when it doesnt send power to the relay it stays on for maybe 3 seconds. When it works how it should, it stays on for 10 seconds maybe. This is another reason that I looked into the relay being bad to begin with